Mesenchymal stem cells (MSCs) are multipotent bone marrow stromal cells aiding hematopoiesis and can differentiate into mesodermal lineage cells such as osteocytes, chondrocytes, adipocytes and myocytes. Thus, they can be utilized as sourced for the development of artificial tissues.
It has recently been reported that MSCs have a potential to differentiate into neuroglia in the brain (Azizi., et al., Proc. Natl. Acad. Sci. USA, 94, 4080-4085(1998); and Kopen., et. al., Proc. Natl. Acad. Sci. USA, 96, 10711-10716(1999)), and therefore, it has been proposed the MSCs can be utilized as sources for the treatment of neurological diseases in the central nervous system (Li et al., Neurosci. Lett., 315, 67-70(2001); and Chen., et al., Stroke, 32, 1005-1011(2001)).
Several growth factors or hormones have been known to induce differentiation of MSCs into neuron like cells. However, those methods have the problem of highly producing non-neuronal cells together with neuronal cells (Sanchez-Ramos., et al., Exp. Neurol., 164, 247-256(2000); Woodbury., et al., J. Neurosci. Res., 61, 364-370(2000); and Deng., et al., Biochem. Biophys. Res. Comm., 282, 148-152(2001)). The problem is more pronounced when the cells are transplanted into the brain of experimental animals (Azizi., et al., Proc. Natl. Acad. Sci. USA, 94, 4080-4085(1998); and Kopen., et al., Proc. Natl. Acad. Sci. USA, 96, 10711-10716(1999)).
Thus, there has existed a need to develop a novel method for higher induction of MSCs into neuronal cells.
Neurogenin and neuroD are the basic helix-loop-helix (bHLH) transcription factors which play important roles in the formation of the nervous system. They form heterodimers with other bHLH transcription factors, such as E12 or E47 and bind to DNAs containing E-box (CANNTG), or on rare occasions, DNAs containing N-box. Such binding to DNA has been reported to be an essential step for the bHLH transcription factors to induce expression of tissue-specific genes (Lee, Curr. Opni. Genet. Dev., 7, 13-20(1997)).
The present inventors have endeavored to develop an effective method for transdifferentiating MSCs into neuronal cells; and have unexpectedly found that MSCs transduced with bHLH transcription factors such as neurogenin and neuroD can continuously express the bHLH transcription factors; and that the MSCs expressing the bHLH transcription factors can be transdifferentiated into a high level of neuronal cells when MSCs are transplanted into the brain of experimental animals.